These cues combine to help form an integrated model of the space. The ability to preview space is noticeably absent without vision and appears to be a major cause of inferior spatial performance exhibited by some blind travelers. Accessing spatial information from a distance gives blind people the ability to preview space and gain information without moving from place to place in active searching. The four environmental cues and spatial abilities (to identify objects up close, to identify objects from a distance, to get directional cues to objects, and to orient the body to the surroundings) give the blind traveler much of the same information available through vision and indicate why this type of system produces such efficient, safe, and less-stressful travel.
The “vision-like” cues made available through location-specific
auditory prompts allow a user to get more complex information about the locomotion
path and more spatial information about the environment. Instead of being limited
to path knowledge, adjacent landmarks can be easily picked up and stored in
memory. In this experiment, this additional information appeared to help
users to structure their mental maps with more relevant and accurate knowledge.
The ability to preview a large space and receive direction and identity
cues appears to greatly increase the speed of compilation of an accurate mental
image of the environment. In addition, the test subjects strongly expressed
the view that the cues received from RIAS gave them much more independence,
and, according to Casey (1978) , independent travel leads to superior mental
representations.
There is little agreement about the spatial cognition, mobility, and orientation abilities of blind people in large scale or geographic space. In fact, three different theories have been postulated to explain the limited spatial skills exhibited by blind subjects concerning the comprehension of space (Fletcher, 1980) . The deficiency theory holds that congenitally blind people do not possess the ability to process spatial relationships, and that the lack of a schema is caused by the absence of visual experience of large and small scale locational properties. This view also holds that some adventitiously blind people have not had time to develop a full spatial relationship understanding and are also unable to develop one.
Another theory is that of inefficiency. It explains that congenitally and early blind people might have the ability to process spatial information, but that they have to use auditory and haptic senses; the spatial system was designed for vision, thus leading to ineffective use of these skills. A blind person might interpret a gently curving path as a straight line or not be able to recognize patterns in the environment.
The third theory, that of difference, states that all spatial concepts are available to all people, but that quantitative and qualitative differences are introduced based on visual experience. Blind people may use different structures to acquire and process spatial information, and they may take much longer to acquire this knowledge. This theory also says that lack of sight may hinder the ability to store, retrieve, manipulate, and use pieces of spatial data stored in the mind (Golledge et al., 1988) . Research, using eight different but supportive approaches to measure spatial knowledge, showed that the blind exhibited the same spatial understanding as the sighted, and that any difference could be due to visual cues that were not available (Passini & Proulx, 1988; Passini, Proulx, & Rainville, 1990) . However, if these visual cues could be substituted for, perhaps there would be no difference in the processing schema.
This leads to a fourth possibility, that of an amodal representation (Carreiras & Codina, 1992) , which postulates that the blind are able to store and process spatial relationships in a manner similar to the sighted, but that it might take them longer. The authors say that the blind can acquire configurational spatial knowledge and solve spatial problems with strategies similar to those used by the sighted, and that mental spatial representations are not limited to any particular sensory modality. Although this experiment was not designed to fully answer which theory is most valid, the amodal theory best explains the present findings. Some of the reasons for the disparities between these different theories and how the chosen experiment was designed to avoid many of these confounds will be discussed next.
There appear to be many reasons why there is such disagreement among researchers about the capacity and abilities of blind people to input, process, store, and use spatial and configurational relationships. Reviews of many experiments and the issue of validity have been covered in great detail in other papers (Golledge et al., 1999; Jacobson, Kitchin, Golledge, & Blades, 2002; Kitchin, Blades, & Golledge, 1997; Kitchin, 1994; Strelow, 1985; Thinus-Blanc & Gaunet, 1997) .
It is not an easy task to recruit a large number of research subjects with severe vision impairments. Much of the research reported in the literature mirrors this difficulty by the use of quite small sample sizes. Many experiments had sample sizes of eight or less per group, and such small samples make it difficult to draw generalizations about the abilities of other blind or vision-impaired people. This research was based on 30 subjects: 17 were congenitally blind, 20 had no useful vision, and another six could only see some shapes. Compared to most experiments of blind navigational skills, this was a large sample size, with a high percentage of totally blind subjects. The subjects were also more homogeneous than some other sample test-groups. They all reported having undergone Orientation and Mobility training, and they were adults who all exhibited independent travel skills by traveling to the test site without assistance. They were a fairly active group, with over half holding jobs and most of the rest receiving training or education.
Much research on spatial abilities without vision is conducted in small scale or even laboratory spaces, yet these results have been treated as if they applied to large scale and naturalistic spaces. These range from tabletop experiments, to room-size (Hill et al., 1993) , to buildings (Passini & Proulx, 1988) , and to artificial mazes (Passini et al., 1990) . Some experiments in larger scale spaces only use several choice points (Dodds et al., 1982) . Only a few have used environmental and natural spaces (Golledge et al., 1999; Jacobson, Kitchin, Gärling, Golledge, & Blades, 1998) . A large-scale environment, as in this experiment, might offer additional cues such as sounds, breezes, and smells that can be controlled in a small-scale experiment. However, uncontrolled environments can be complicated by the presence of people, obstacles, and other distractions.
Skilled blind travelers process and use many non-visual cues during their daily
navigation, yet some large-scale tests are conducted in a featureless and cue-less
open field, with irregular turns being required at non-distinct choice points,
causing concerns about ecological validity. Strong evidence of
the spatial skills of the blind (Golledge et al., 1999; Jacobson et al., 1998)
is due in part to an experiment design that allowed blind people to use cues
at choice points that were familiar, typical, and memorable, instead of being
abstract or featureless locations. The experiment reported here was also
conducted in the type of built environment familiar to blind travelers; they
were tested in a large interior space of a transit terminal, along city streets,
and crossing streets to other transit modes. No scale transformation
of these findings is claimed; the results are attributed to these everyday environmental
spaces. This is where the blind labor to achieve independent navigation;
they do not do so in small scale or laboratory space.
Mental map information and configurational knowledge must be
extracted by using external products that attempt to portray the internal
knowledge stored in the mind. While sketch maps might be adequate to
capture this internal knowledge for the sighted, lack of vision and familiarity
with drawing make this type of spatial product invalid for blind research.
This is well understood, but other products are also not familiar or accessible
to the blind. Pointing to landmarks in the environment might be flawed
if the person has rotated their position (such as a turn toward the experimenter’s
voice) or otherwise is not sure (during the pointing task) of their alignment
to the path they are on, and these errors in orientation might produce results
that do not reveal their true mental representation. Even 3-D models,
while far superior to sketch maps, can be flawed because people must search
for, identify, and scale different segments or pieces without the use of vision.
Some people have a poor understanding of metric distances, and a product
that uses distance estimations can result in an “impossible” map
when using typical multi-dimensional scaling techniques. Even spatial
relationship questions might be biased toward vision, or prior visual experience.
If these tests or spatial products do not measure what they are intended
to, without error, there are construct validity issues that might affect
the different theories about spatial abilities. In this experiment, two
spatial products were used to reveal spatial and relational knowledge: the ability
to understand and use shortcuts and the relationships between objects that they
had recently visited.
The experimental design that stressed the utility of tasks and tests was discussed earlier (see Section 4.6 , Spatial Knowledge Acquisition and Cognitive Maps ). The utility to get from one point to another in a complex real world environment tells more about a person’s spatial skills than does comparing revealed spatial knowledge to objective, often Euclidean, reality (Kitchin & Jacobson, 1997) . Mentally intensive estimations of distance or directions might fail to reveal the internal map as well as might the use of a more real-world and high-utility approach.
Different tests designed to measure distance cognition have been found to yield different results (Montello, 1991) . With so many imperfect ways to elicit internal spatial knowledge, it is quite important to test blind people’s knowledge with more than one method. If two or more methods or tests are used, and they do not agree, then one or both of those methods is suspect or invalid. Some of the research that is cited as supporting these differing theories of spatial organization uses only one method to measure spatial skills. If only one is used, there is no way of knowing if it is a valid choice. Kitchin & Jacobson (1997) believe that each spatial test introduces some bias into the analysis, and that multiple and mutually supportive tests must be used to more completely assess configurational knowledge. This lack of methodological convergence (Campbell & Fiske, 1959) makes much of the cited literature suspect as to the validity of the different theories. The experiment presented here was not designed to fully investigate spatial skills, but two methods were used to estimate spatial knowledge, and both methods converged to show that RIAS users had superior spatial awareness. In addition, many people in the RIAS condition had perfect or near perfect results, which were not seen in those who used their regular methods. In addition, the field test showed that path travel times, error production, and request for assistance were all superior in the RIAS condition.
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